Voyager 2 at Uranus, 25 Years Ago Today


Voyager 2 is the only spacecraft that has flown close by one of the more enigmatic planets in our solar system (and the butt of many one-liners): Uranus. It was 25 years ago today (Jan. 24) that Voyager made the close pass, and scientists from JPL have been reminiscing about how they pored over the data being returned by the Grand-Touring Voyagers.

“Voyager 2’s visit to Uranus expanded our knowledge of the unexpected diversity of bodies that share the solar system with Earth,” said Project Scientist Ed Stone, who is now based at the California Institute of Technology in Pasadena. “Even though similar in many ways, the worlds we encounter can still surprise us.”

Voyager 2 has discovered two "shepherd" satellites associated with the rings of Uranus. Image Credit: NASA/JPL

From the flyby, we saw for the first time Uranus’ small group of tenuous rings, and the tiny shepherding moons that sculpted them. Unlike Saturn’s icy rings, they found Uranus’ rings to be dark gray, reflecting only a few percent of the incident sunlight.

Miranda, innermost of Uranus' large satellites, is seen at close range in this Voyager 2 image, taken Jan. 24, 1986, as part of a high-resolution mosaicing sequence. Image credit: NASA/JPL

The images also showed the small, icy Uranus moon Miranda that had a grooved terrain with linear valleys and ridges cutting through the older terrain and sometimes coming together in chevron shapes. They also saw dramatic fault scarps, or cliffs. All of this indicated that periods of tectonic and thermal activity had rocked Miranda’s surface in the past.

The scientists were also shocked by data showing that Uranus’ magnetic north and south poles were not closely aligned with the north-south axis of the planet’s rotation. Instead, the planet’s magnetic field poles were closer to the Uranian equator. This suggested that the material flows in the planet’s interior that are generating the magnetic field are closer to the surface of Uranus than the flows inside Earth, Jupiter and Saturn are to their respective surfaces.

Voyager 2 was launched on Aug. 20, 1977, 16 days before its twin, Voyager 1. After completing its prime mission of flying by Jupiter and Saturn, Voyager 2 was sent on the right flight path to visit Uranus, which is about 3 billion kilometers (2 billion miles) away from the sun. Voyager 2 made its closest approach – within 81,500 kilometers (50,600 miles) of the Uranian cloud tops – on Jan. 24, 1986.

By the end of the Uranus encounter and science analysis, data from Voyager 2 enabled the discovery of 11 new moons and two new rings, and generated dozens of science papers about the quirky seventh planet.

Voyager 2 moved on to explore Neptune, the last planetary target, in August 1989. It is now hurtling toward interstellar space, which is the space between stars. It is about 14 billion kilometers (9 billion miles) away from the sun. Voyager 1, which explored only Jupiter and Saturn before heading on a faster track toward interstellar space, is about 17 billion kilometers (11 billion miles) away from the sun.

“The Uranus encounter was one of a kind,” said Suzanne Dodd, Voyager project manager, based at JPL. “Voyager 2 was healthy and durable enough to make it to Uranus and then to Neptune. Currently both Voyager spacecraft are on the cusp of leaving the sun’s sphere of influence and once again blazing a trail of scientific discovery.”

Click on the images above to see higher resolution versions on JPL’s Photojournal website. Or see this link on the Photojournal to see all images of Uranus.

Pluto Spacecraft Gets Brain Transplant


Still seven years away from its rendezvous with Pluto, the New Horizons spacecraft was awoken from hibernation for the second annual checkout of all systems. The spacecraft and its team back on Earth will also undergo three months of operations as the New Horizons will make observations of Uranus, Neptune, and Pluto. But the first order of business was uploading an upgraded version of the software that runs the spacecraft’s Command and Data Handling system. “Our ‘brain transplant’ was a success,” says New Horizons Principal Investigator Alan Stern. “The new software – which guides how New Horizons carries out commands and collects and stores data – is now on the spacecraft’s main computer and operating, over a billion miles from home!”

The mission ops team at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, radioed the software load and the commands to start it earlier this week through NASA’s Deep Space Network of antennas to the spacecraft, now just more than 1.01 billion miles (1.62 billion kilometers) from Earth. In the next 10 days the team will beam up additional new software for both the spacecraft’s Autonomy and Guidance and Control systems.

Space Science Mission Operations Center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.
Space Science Mission Operations Center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

Alice Bowman, New Horizons mission operations manager at APL, says the spacecraft and its computers are healthy. “The new software fixes a few bugs and enhances the way these systems operate, based on what we’ve learned in running the spacecraft in the nearly three years since launch,” she says. “They also configure the onboard systems to be ready to support the Pluto-Charon encounter rehearsals scheduled for next summer.”

New Horizons is more than 200 million miles beyond Saturn’s orbit and more than 11 astronomical units (1.02 billion miles) from the Sun, flying about a million miles per day toward Pluto. Annual Checkout 2 (ACO-2) continues through mid-December; follow its progress through frequent updates on the New Horizons Twitter page.

Source: New Horizons Press Release

Podcast: Uranus


This week, we’re on to the next planet in the solar system. Having only visited it up close once with Voyager 1, we don’t know much about this sideways-spinning ice giant. But today we’ll cover what we do know, including its faint rings, sideways axis of rotation and rocky core – a first in the gas planets we’ve encountered so far in our tour.
Click here to download the episode

Uranus – Show notes and transcript

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Uranus’ Rings Seen Edge On


Once every 42 years, the angle between Uranus and the Earth is perfectly lined up so that the planet’s rings are seen edge on. Since the rings were only discovered back in 1977, this is the first opportunity astronomers will have to view the planet without the glare and dust from the rings. It doesn’t happen on a specific date, though, it’s a little more complicated than that.

Because the Earth goes around the Sun much more quickly than Uranus, there are actually three separate times that Uranus and the Earth line up perfectly: May 3 and August 16 in 2007, and then February 20 in 2008. Unfortunately, during that last point, the Sun will be directly in between our two planets, so we won’t be able to see Uranus.

The first to image Uranus during this special occasion was a team of astronomers from UC Berkeley. They imaged Uranus on May 28th with the near infrared camera and adaptive optics on the W.M. Keck II telescope atop Hawaii’s Mauna Kea. Their images revealed the nearly edge on ring appearing as a bright line passing right through Uranus.

The next images come from Hubble, taken on August 14th. Hubble captured its images on nearly the precise moment when the rings were aligned with the Earth, showing similar features to the Keck image, and also seeing some recently discovered outer rings. The outermost ring, seen by Hubble, is difficult to view in infrared.

Astronomers are hoping these images will reveal more details about the moons that help tend the ring, called Cordelia and Ophelia, keeping it in place. But it’s also thought that there are additional moons in the region, helping to tend all 9 rings. This precise geometry might allow the telescopes to reveal moons that would normally be lost in the glare of the rings.

One other important date:

“December 7 is the Uranian equinox, when the rings are perfectly edge-on to the sun, and after that, there is a brief period again when we will view the dark side of the rings, before they become illuminated again for another 42 years,” said Heidi B. Hammel of the Space Science Institute in Boulder, Colorado.

Original Source: UC Berkeley News Release

Dark Spot in Uranus’ Clouds

The Hubble Space Telescope has discovered a giant cloud vortex in the upper atmosphere of Uranus. This cloudy feature measures 1,700 kilometers by 3,000 kilometers (1,100 miles by 1,900 miles) – large enough to engulf 2/3rd of the US. Although rare on Uranus, these cloud spots are actually quite common on Neptune, since the ice planet has a much more active atmosphere. Since this region of Uranus’ atmosphere was previously in shadow, astronomers theorize that heat from the sun created the vortex.
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Hubble Sees a Rare Transit on Uranus

The Hubble Space Telescope recently captured a very rare event: the transit of its moon Ariel across the surface of Uranus. On Earth we call this an eclipse, when the Moon’s shadow falls upon the surface of our planet. This situation is rare on Uranus; however, because the blue-green planet is tilted over on its side. The Sun, the moons and Uranus only line up once every 42 years. The last time a transit like this could have been seen was 1965, but Earth-based telescopes weren’t powerful enough to image the event at the time.
Continue reading “Hubble Sees a Rare Transit on Uranus”